I think the iPhone 5 is the oldest "supported" iPhone, and that you need iOS 10 or later to run the DPA app (I am using an iPhone 6S +).
I have experimented with my Android phone (an LG V30); you can't reset the volume without the iOS app of course. While recording at home with USB Audio Recorder Pro on my Samsung Galaxy Tab S3 tablet with no screen shut-down works fine and rolls over files seamlessly at 2GB, the LG phone using USB Audio Recorder Pro with the screen blanked stops after 2 GB (it looks like it is recording but no file is saved beyond 2GB). This may be fixable, I have not tried further tweeking. But I wouldn't want to buy any combo that hasn't been attested to work with the hardware you want to use, for the length of time and resolution you use.
It would really be nice if the DPA app recorded as well, and were available for Android.