TMobile Home Internet causes phones to not work

I carried my Nokia modem  around the house and only see 2 bars from the tower.There are 3 towers,2. about 1000 meters and one at 600 meters.Presently the modem is in the basement running my TV on5MHz and VoIP phones(3) and security cams(4) on 2.4 MHz. and all work fine although my ethernet speed is only about 80 mbts and 2.4 GHs wireless around 20 Mbits and 5MHz wireless is around 60mbits.Tmo used to have a signal booster available which would be a help as I,m not too crazy about disassembling my modem to add an antenna..