lost app store on iphone

The usual reason for the App Store app not being visible is due to a restriction having been placed on purchases. See: Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support

If that isn't the solution, try using Search to locate it: Use Search on your iPhone, iPad or iPod touch – Apple Support

Sorry, I don't know of anything else to suggest. It is not an app that can be deleted and I've not heard of any cases where it was.