[femto]

The LTE protocol is asymmetric between towers (eNodeB) and phones (UE).

You could build srsRAN and run a local eNodeB instance to form a local LTE network. Given that it has a radio that operates in the LTE bands, in theory you might be able to build srsRAN for a phone and run the necessary base station software (eNodeB and EPC) on a phone to form an "ad hoc" network. It wouldn't be truly ad hoc in that the network would still have a base station, just that it would be running on phone hardware. srsRAN wouldn't be running as an application, but would be replacing the firmware in the phone's LTE modem.

Edit:

Here is a paper by someone who has built an ad hoc LTE network.

https://arxiv.org/pdf/1802.09262

It does exactly the above: using srsRAN (which used to be called srsLTE) to run local base station software (eNodeB+EPC) to get around the asymmetry in the LTE protocol.