Does my phone have hidden tracker app

iOS / iPadOS devices cannot be hacked or infected with Virus / Malware / Spyware if it is updated to latest iOS/iPadOS, unless you have intentionally downloaded spurious softwares or unauthorized apps directly from the internet and installed on your device or/and have Jail Broken. 

It (Hacking) also depends on how careful are you in sharing sensitive and valuable information pertaining to your iPhone such as Passcode, Password etc with your friends and family members.

Be careful when sharing the device's sensitive and valuable information with friends and family members.

Thumb Rules:

1. Enable  Guided Access before handing over an iPhone to kids
2. Don't share Apple IDs
3. Don't Jail Break
4. Don't share sensitive information pertaining to your device and payment methods
5. Beware of Phishing

Settings ? Privacy > Tracking. Here you can turn off the ability to allow apps to request to track you across apps and websites owned by other companies