Most water you’d drop a phone into has enough traces of salt to make it conductive. Therefore, the water acts like a faraday cage.
Theres a calculation you can do to calculate this, its pretty standard E&M stuff. Basically you calculate the skin depth of the material and thats as far as the signal can penetrate. The derivation highlights some cool things:
1. Its frequency dependent. This is why military submarines communicate at around 30 Hz.
2. Your audio cable (and all high frequency power cables) are stranded
3. Your microwave is effectively shielded with a thin layer of metal
4. An induction stove wont work with Al pans, but will quickly melt Al foil
Theres a calculation you can do to calculate this, its pretty standard E&M stuff. Basically you calculate the skin depth of the material and thats as far as the signal can penetrate. The derivation highlights some cool things:
1. Its frequency dependent. This is why military submarines communicate at around 30 Hz.
2. Your audio cable (and all high frequency power cables) are stranded
3. Your microwave is effectively shielded with a thin layer of metal
4. An induction stove wont work with Al pans, but will quickly melt Al foil