So... I struggled with this for a bit. I have a Galaxy Note 5 and I didn't want to spend the money on the Phoneskope. I also didn't want to have to take my regular case on and off. I looked at DIY options and wasn't really satisfied with anyone of those. I also had a universal mount that I would leave my case on my phone and use on my scope but it was clunky and never really lined up.
What I ended up doing was buying the Phoneskope and taking my case on and off. It's not too big of a pain and it works extremely well. I still think its an overpriced piece of plastic, but I bought it anyway. The nice thing is that its two pieced: one specific for the phone and one for the scope. So if you ever get a new phone, it'll only cost about $40 to get the new case for it.