Mobile Uplink

As claimed by Supergirl during the broadcast of Meet That Hero!, E.T. was in possession of a phone which could get "crazy coverage", with which he could call his "crew of intergalactic botanists". It appeared similar to a vehicle which E.T. once flew through the air on.

History
E.T. once stood next to the phone in a field.

At another point, he indeed called his crew while standing in (WC: Supergirl Meets E.T.) the Land of Oz. (PROSE: Halflife, Normality, Dead Romance)

Behind the scenes
Although unnamed in Supergirl Meets E.T., the device shown was the "Mobile Uplink", an alternative form of "Phone Home", which appears in LEGO Dimensions.