Thank you, I already read the walkthrough and went to the La Grande several times now after I got the "Beautiful Dress" but Philipp never showed up. Is there a specific day when this happens?
It was a long time ago, and I won't tell you the exact day, but it's likely that by presentation in the walkthrough the author means Monica's 1st presentation (there's also a 2nd, later). In the screenshot below, this quest from the Office storyline is circled in red.
Make sure you have this quest completed (in the main storyline "Office") and then send Monica to the restaurant of the Hotel Le Grand and let her order her food, after which Philip should approach her. In general, progress in this game is somewhat directly related to progressing through the main storyline. So if you're concentrating on the side storylines and you're not getting anywhere, universal advice is to make sure your Monica has progressed sufficiently through the Office/Photo Shoots storylines.