If you've been sent an .ipa file from your developer, and want an easy way to install it on your phone, then you can use this site to easily install this app on your phone.
Install IPA on iPhone or Android would be using online web service Install On Air. You can simply upload your IPA file for iOS to Installonair website and it will generate a link. When you open the link on your iOS device web browser, it will ask you if you want to install the app. Then you just tap on it to confirm the installation.