My experience with ImageSync and my K-70 is that it can be flaky on a bad day … WifiCommander
Wifi Commander for Pentax - wireless remote control for your Pentax camera is a more reliable solution, but that's for a pc, not a 'phone. I don't believe there's another suitable 'phone app available.
One important factor, (not just with the K-70), is to ensure the 'phone you're using has been configured to
ONLY use the connection to the camera and not to go wandering off looking for any other network.
Obviously the 'phone will need to be reset to "normal" operation when you've finished playing with your camera.
My personal opinion is that ImageSync was primarily intended as a wireless remote control, with the ability to revue the odd shot, not as a total image handling solution. I never have more than a day's worth of images on my card, so I've never been in a situation where the app has needed to handle a great number of pictures. If transferring images off the card is not an immediately available option, maybe an extra card or two might make for easier management.
Being really close to the camera when trying to transfer data will improve things significantly, especially in a domestic environment where there is likely to be other devices effectively causing interference.
Just wondering which manual came with your camera?
I believe some cameras were only issued with a relatively brief introductory guide, whereas mine was supplied with the full 156 page Operating Manual, including nine pages about using the wifi connection.
If you don't have the latter, it's available as a pdf download here
Operation Manuals Download : Support & Service | RICOH IMAGING
Good luck