forece_rport is not a valid option! Could you explain why you need the nat option, as, if really needed, it indicates a significant, unusual network configuration. NB If Asterisk is behind NAT, you need to tell it how to find its public address and nat= does not do that.
The only devices you have identified are the soft phone and the mobile. I assume the mobile is connected through the mobile network, so I don’t understand why being in the same office is relevant.
Also, you haven’t provided any part of sip.conf that relates to devices in the office.
You should also note that chan_sip is now deprecated, so you should be trying to reproduce this on chan_pjsip.
Do you have a licence for the G.729 codec? If transcoding becomes necessary and you don’t, you could end up with no audio.