The iPhone provides a great degree of control over what information you share in Settings > Privacy

Location Services shows you which apps you have allowed access to your location, you can revoke any you no longer need

Most apps now default to 'While Using the App', but some may have 'Always' access - you can change this here

You can see which apps can access your Contacts, Calendar and Reminders and turn them off if you've changed your mind

You can block apps from accessing your Photos, or some only request the ability to add new photos not see other ones

Microphone and Camera access are also worth checking

You can further fine tune access to Bluetooth Sharing, Speech Recognition, Health, Homekit, Media and Motion data

You can choose if you want to share analytic data with Apple or third parties

To reduce online ad tracking, turn on Limit Ad Tracking. You can Reset Advertising Identifier to clear previous tracking