Get IPA installed on my phone

I got a developer to develop an IOS app for me. He sent me the IPA. Now my problem is I am not able to get it installed on my phone to try it. I have IOS 8 iphone and ITunes 12.1 (I have both Mac and Windows). On the iMac, whenever I double click on the IPA and click on install/sync, it keeps saying installing.

I read so many posts about alternate methods but they seem outdated or I am missing something.

Can you please tell me how can I get the IPA installed on my phone?

Thank you

PS: I am android developer so this ios terminology thing is new to me