Using proton mail on your phone you have the possibility to consult your contacts.
But it is not easy to access. In addition we see only the name of the contact and email address, to see more info you have to develop. A great improvement would be to see the name, email, and main telephone number immediately.
So it would be very easy to use only Proton to keep up his phone contacts, and abandon the other apps that are not safe from indiscretions.

The best would be that this is a little faster than currently...