Why is there a ? mark over the image of my phone on my finder of my Mac?

Checkout this reference from a previous post:

Welcome to Apple Discussions!!

It looks as if something has gone wrong with "Customise Toolbar". Try re-doing this: with the relevant Finder window at the front, choose "Customise Toolbar…" from the "View" menu. Then "drag the default set" to the window toolbar, and select "Icon Only" in the "Show" pop-up. Click "Done" and your question mark should be gone.

Check out this link from Apple:

If your device doesn’t appear in the sidebar when connected to Mac - Apple Support

Here is the link to the above post to see it in full.

https://discussions.apple.com/thread/1144923?answerId=5409577022#5409577022

Sorry if that did not work, I have nothing else to add.