There is not s straightforward answer to this. In open space with no objects between Safelet and Phone we have measured a distance of 40 meters. However this was dependent of the type of Phone also. With a Samsung S6 we measured a greater distance than with an iPhone. In general the distance with iPhones was smaller.
To complicate things, these distances cannot be accomplished indoor. Indoor distances are very dependent on the structure of the location. For example the structure of the walls and ceilings ( wood, concrete, metal or a mix ) plays a very important role. In general it is not possible to claim any measure of indoor distance.