Hello, Trevor' Go to settings > Security and 'uncheck Unknown Sources' This will stop the phone from installing apps from all unknown source except Google play store.
If there is a rogue app that is forcing google play store to download and install apps without your permission' please follow the instructions below to stop it.
- Go to settings> apps/application and navigate to play store
- Touch clear cache and data.
- Touch the home key and then open Google play store
- Don't check 'keep me up to date' touch accept and then Get started.
- Open Google play store.
- Touch the 3 dots top left of your phone screen or touch the more option/action button below your phone screen and choose Settings.
- Touch 'Auto update apps' and select Do not auto up-date apps.
- Scroll down to 'Parental control' and turn it on.
- Enter your pin code.
This will stop any rogue app from pushing play store to download and install apps without your permission.