Probably Philippe lacked the right strength of nerves or innate military ability to have made a success of personally leading the army in battle - at least as implied from his past conduct before 1789, such as his fumbling behaviour in battle as a senior naval commander in the American Revolutionary War vs Britain in 1778 when he is supposed to have missed a chance to exploit a gap in the British line of battle. He was no Nelson - too much a privileged noble who had had rank handed to him on a plate, as his foes could allege? Also he gave up on the Revolution at one point and fled to the Austrian Netherlands in 1791, then changed his mind and came back, which suggests that he was unsure of running risks in the cause of principle or ambition - which could well have returned to make him dither at some crucial point in the swift-moving events of the early 1790s. This incident is supposed to have cost him much of his original Jacobin backing of 1790-1; if he had been more resolute his chances of 'riding the tiger' (for a few years at least) as a 'Citizen King' at the head of a faction-prone Assembly in 1792-3 would have been higher.
I would guess that if he did manage to get elected as a constitutional King by the Assembly after Louis fled, he would have been good at making appropriately democratic gestures, eg signing radical laws and going along with anti-Catholic legislation and Church purges, and popular with the Paris crowds - at least unless and until the war started going wrong. Until then the cause of the Republic would have been far weaker than in OTL as the monarchy would seem to be at the head of the revolution not betraying it, he would not be vetoing many if any laws, and as a liberal King any new emergency govt required to fight a mixed crisis of civil war and the Austrians approaching Paris would be a Royal cabinet with him at the head of it, not a self-running 'Committee of Safety', as he would be thought trustable by the Assembly. There would be no legitimate excuse for any uprising in Paris against an 'incapable' or 'treacherous' govt, and possibly crucial figures in organising the OTL one would be in govt by Sept 1792 (Danton in a position to use his vocal skills encouraging citizens to join the army, Robespierre as an administrator behind the scenes?) albeit subject to royal vetoes and Philippe stopping them from running a bloody purge of enemies - and unhappy with this?
Whether Philippe had the skills to attract moderate Jacobins, professional administrators who put practical success above ideology, and personal foes of Robespierre (eg Carnot and the future post-Thermidor leadership?), or even Danton, to back him and box R in is another matter. But if he had the fickle populace 'on side' as a man who mingled with the people, lived fairly simply, and joined in their festivities (and the new Cult of Reason?) wearing a Cap of Liberty, there would be no huge crowds to back any republican coup as in August 1792 in OTL. His popularity could well scare most of the Jacobins off trying to replace him , with them deciding to save France from the exiles and the return of a live Marie Antoinette at the head of an Austrian army (a useful bogey-person to stir up the public) first and deal with the long-term issue of the monarchy later.
With luck and no major mis-steps in the crisis of the war and/or with Lafayette reluctantly putting the safety of France first and acting as a successful commander-in-chief, Philippe could have served as a block on a full 'Terror' in 1793-4 (eg by keeping the Girondins in his ministry as a balance to the extreme Jacobins) and divided the OTL 1793-4 republican factions by causing a major pro- and anti-monarchic split - which of them would join his regime to save France and which would stay out of office as they don't trust any King? The monarchy could fall later as the political leadership split over the question of aggression against their defeated foes and the 'international Catholic reactionary coalition' or whether to annex the Netherlands or Italy. Or would the most extreme Jacobins (St Just?) try to assassinate the King to save liberty from a 'dictatorship' by the moderates and thus provide an excuse for a military crackdown on them? If Philippe is assassinated by republicans in a botched coup, would his inexperienced son be pushed aside as unable to run a country in wartime and a plebiscite on the monarchy be promised for peacetime then 'forgotten about' deliberately? In the meantime it would be Louis XVI and his wife who would be serving as the nominal rallying-point for the exiles and the Austrian-Prussian alliance during the 1792 invasion, probably from the Rhineland or Brussels, and then if military events follow their OTL course the ex-queen's Habsburg links would probably see them take refuge in Vienna in 1794/5. The Jacobins could then concentrate their propaganda on her as a evil mastermined - as the republicans of 1917 Russia aimed at Czarina Alexandra 'the German woman' and her past involvement with Rasputin.
I can see an equivalent of the real life travails of the British royals in the 1650s, when the French queen mother Henrietta Maria (as widow of Charles I) and her son Charles II were initially backed by her French kin against Cromwell for the 1650-1 Stuart expedition to Scotland but after Cromwell's victory and his Commonwealth's 1655 treaty of peace with France Charles II had to leave the latter. (He ended up as a Habsburg pensioner in the Netherlands in 1656-60.) In this case, the Habsburg emperor Franz II would have given MA and Louis plus their children sanctuary but after the treaty of Campo Formio with republican France in 1797 they would have had to leave - would they have ended up in Russia as pensioners of the Romanovs? And driven out of there by Napoleon in the 1807 Treaty of Tilsit? In real life Louis XVI's brother Louis XVIII was based in the Russian-run Baltic states at Mitau (Latvia) until then and the ended up in England - as Louis XVI had fought England in the US in 1778-83, it would be ironic if he had to seek safety with his old foe George III in 1807-8. But given his mixture of a poor reputation in France, as the attempted betrayer of the Revolution , even if his wife was dead by spring 1814 would the British have dared to try to risk putting him back on the French throne or would the French elite have accepted him ? (He would have been nearly 60, but most of his ancestors who had died younger had done so in epidemics, been in worse health than him, or been assas; his gt-grandfather Louis XIV lived to 76.) Would he have seen sense or been told by the Prince Regent and his generals to abdicate in the name of his son Louis XVII, then aged 29 (born 1785), and would the latter have been better able to keep his throne than the reactionary Charles X?
