Ability to find php developers is usually a reason to choose php. It's actually harder to find good js developers.

Javascript frameworks work nicely with php acting as an api. An even better approach is a hybrid that allows you to use a framework like Vue/React or a libruary like jQuery but also allows you to use php to power your pages. This gives you the ability to have an spa per section.

A common approach is to use an api to deliver data to your mobile app. If you've built it in php that can be reused.