seems you cannot register on Ile de France mobilités app without a mobile French number
1 answer
I'm wondering if you've been redirected to creating a "resident" account for a personalized Navigo card (which definitely does require a local French number and residential address) and not a Navigo Découverte card, meant for visitors and people who do not want a personalized card.
Can you try creating an account on their website while using a private session on your browser (so there are no cookies related to creating a personalized, resident Navigo card) at https://mon-espace.iledefrance-mobilites.fr/ and see if that asks for a phone number? (It shouldn't, I just reverified with my own account, which only asks for email, first/last name, no phone number is possible to add.)
This account created through the website listed above can be used to login to the "My space" section of the Ile de France Mobilités app.
Please let me know how you make out.