Hello Sand_ipe,
Thanks for visiting Apple Support Communities!
I understand you are concerned about your dad's iPhone having access to your iCloud Photos. If it appears that your father's Apple ID may still be associated with your iPhone, you may want to double-check the Apple ID settings outlined in the following article:
Sign in with your Apple ID - Apple Support
If your iPhone was previously your father's, and even after checking the settings in the above article you are still having issues, you may want to verify that the steps taken in the following article were done before it was transferred to you:
What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support
Also, depending on exactly how your father is seeing your photos (all photos you take, or just specifically shared photos), you may also want to check your photo sharing settings:
Use Shared Albums in Photos - Apple Support
Best regards.