This app was mentioned in 3 comments, with an average of 2.00 upvotes
I'd use tinc to see if it works:
https://play.google.com/store/apps/details?id=org.poirsouille.tinc_gui
There's also an openvpn installer on github I've used lots of times:
Head over to Digital Ocean. Sign up. Spend $10. Spin up a $5 instance of Ubuntu. Setup a Tinc VPN server.
Install Tinc on your phone and on all the clients you wish to connect together be they Windows or Linux (apt-get install tinc etc) point them all at your newly created tinc server and you can reach all your machines anywhere in the world.
Good luck!
It requires root on android. https://play.google.com/store/apps/details?id=org.poirsouille.tinc_gui&hl=en_IN
Windows and mac are also listed under - https://www.tinc-vpn.org/platforms/.