I have discovered that the UK’s phone signal is terrible. I expected poor connectivity on coastal paths in Cornwall, but everywhere I went I experienced problems.
and it is harder for phone signals to penetrate the more energy-efficient materials in new buildings.
Is that so? Which material is that supposed to be? Neither styrofoam nor rock wool does anything to them. Bricks, on the other hand, do, just like concrete.
Not in the UK, but Arizona in the US. A lot of low energy materials have linings that block signals significantly. They're meant to help insulate but a lot of the properties that do that also block signals. It's all EM radiation, just different wavelengths.
Modern Low-E windows linings meant to help insulate will block phone signals quite substantially compared to the past. Saw the changes happen firsthand over the last 20 years selling and repairing phones.