Can I have multiple Online Soccer Manager (OSM) 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 OSM and create a second account.

4. Click on the cloned app, log into your second OSM account on the cloned app, and you're good to go!