I looked in to this Pnats and actually got set up with the visual only (no head tracking) VR using my phone and a Google cardboard kit - it isn’t very good.
I used a Google Cardboard kit (2x 45mm lenses, magnet slider, velcro strap), an LG G5 and the free Trinus VR software tested with one of the Homeworld games.
It is supposed to allow you to use it over Wifi or via USB connection to your PC but I was never able to get the USB connection to work after trying over a couple of days so had to use the Wifi. Over wifi, unless you have a particularly fast wifi setup, your average homehub wifi will result in a silly amount of latency.
At the time I was using it with a Sky router (pre-Skyhub) sat less than 3 feet away from it and had a lot or problems with latency which made the game difficult to impossible to play because of the input lag and made me feel really, really motion sick - though I think the motion sickness was only in part due to the latency.
Setting up your phone is not remotely intuitive either, with you having to set all of the scaling/wrapping/screee mapping/edge/distance/etc settings to get it to work with your sized phone screen and then the array of other settings that might as well have been in cantonese for all they meant to me. I was lucky enough to find a screenshot someone posted with decent settings for the LG G5 but I’d have just had to trial and error it otherwise.
It might have changed some by this point, I’m talking 2/3 years ago I think, but the state of the software when I was using it was not especially hand-holdy and the USB connection just flat out didn’t seem to work.
And all that was before the pot luck that is Android accelerometers with the separate head tracking software.
If you have a flagship Android phone, don’t mind spending £20 on a cardboard kit and have time to burn, try it out, but it’ll be a bit of a project getting it going and you might well be disappointed.
For more info, google ‘Occulus Thrift’ and look at the various articles/guides that were floating about a few years back.