Can I open multiple EA SPORTS FC™ Mobile (FC Mobile) accounts on one phone at the same time?

sure. You can use matrix cloning.

Use matrix cloning method:

1. To install Matrix Clone, you need to download and install it from the Matrix Clone official website.

2. Click the “+” button in the upper right corner of the Matrix Clone application

3. Select EA SPORTS FC™ Mobile (FC Mobile) and create a second account.

4. The application’s icon will now appear on Matrix Clone’s homepage

5. Click on the new application icon in Matrix Clone; this will launch a new instance of the application and allow you to create a second account