In many cases, your phone is just a router in between two others.
But, being a router, you can look at every single packet if you have the ability, skill and tools.

Most internet communications do not happen in clear text.
So, you will have to break the encryption, or know at least about how the packets are formed.

Meshnet is a concept that several groups are working on.
They can explain it far better than i, so you will need to seek them out for the app and the usage.