How to make pdf of photos in phone?

This is actually quite easy, and you often don't need a special app.

On most Android phones, simply select your photos in the gallery. Tap the 'Share' icon and then choose the 'Print' option. In the printer destination menu, you should see 'Save as PDF'.

For an iPhone, select the photos, tap share, and then print. When the print preview appears, use a two-finger 'pinch out' gesture on the thumbnail. This will convert it into a full PDF that you can share or save to your Files app. It's a very handy, hidden feature