How can I find out who else is on my phone connected

No one is connected with your phone. If you share an Apple ID with someone they can see anything that you sync to iCloud and some things on your phone (such as your recent call list, calendars, reminders, contacts, etc).

Here’s how to see if others have access to your Apple ID→Checklist: If you want to see if anyone else has access to your device or accounts - Apple Support