You need help from Customer Support to disconnect you pass from your current phone if you get a new phone. Use the form in the link to make your request. Add your pass number and the start date of your travel to the request.
https://eurail.zendesk.com/hc/en-001/requests/new
Do you have a UK or a Swiss passport?
You will never have the reservations in the app as reservation are separate from the app.
Here is some useful information from the experienced travellers in the Community regarding both planning, reservations and activation of pass and travel days.
Planning
The rail planner is normally not up to date, as it only is updated once a month, so to be sure of the time table you better check the timetable and availability on the websites of the national railways. The bigger national railways, like DB (Germany) SBB (Switzerland) and ÖBB (Austria) cover several countries.
Reservations
The advice from the experienced travellers in the community is to use other ways to make reservations than the Interrail/Eurail website. You can look at the guide in the link:
https://community.eurail.com/train-connections-reservations-47/how-to-get-reservations-105
If you, after having looked at the guide, have questions about how to make specific reservation, please give your travel details (departure date, time and route) preferably in a new topic, and you will get advice.
Please note that Interrail/Eurail charges an extra fee of 2 EUR per person and ticket in addition to the fee for the seat reservation.
Activation of pass
During the activation process, when you choose the start day of the validity of the pass, the first day of the validity period is automatically made a travel day, even if you don't enter a journey, the advice is therefore not to activate the pass before the first travel day as you only can deactivate the pass before 00.00 on the day the validity starts. If your travel plans change in the last moment you will loose travel days if you have activated the pass in advance.
It can be wise to make a test and activate the pass with a start date well in the future and then deactivate the pass immediately, just to see that everything works.
Activation of travel day
The advice from the experienced travellers in the community is also never to activate a travel day, that is connect a journey to your pass, until just before boarding the train, otherwise you might loose a travel day if your travel plans change in a late stage You can't delete a travel day in the past. A travel day can only be deleted until 23.59 CET the day before the travel day.
@AnnaB
Wow thank you so much for your answers!
Regarding my new phone, how can I request help from Customer Support if I don’t have a travel start date yet since it's not been activated? Do you suggest I activate the pass with a date THEN request help, THEN deactivate the pass on my new device?
I actually have a French passport, and neither UK or Swiss.