If you are experiencing digital harassment or online stalking please see this page.
If you think your phone is hacked, or has a tracker and you can not afford to get a new one AND you don't plan to press criminal charges (if you want to / need to do NOT wipe the phone, get it to cops or digital forensics people ASAP).
Honest best thing - buy a new phone. if you can't then try the following.
Most partner hacking I have heard of is app based, using that assumption:
backup images and contacts
make sure you are on your OWN phone plan
reformat SD storage if it has a card
factory restore the device
turn off the device as often as possible to avoid apps geo-tagging you and giving away your location
some things can track a turned off phone
Did you know every image you take and post, and many social media sites, give away GPS coordinates you can't see but others can use when you post?
you can try a cell phone blocking wallet/purse but the quality and efficacy varies
only re-install apps you use and know what they are
please don't root your phone