Idle line voltage is typically 48 to 50V DC, and the ring voltage is low-frequency AC superimposed on that. Voltages vary depending upon line lengths and the number of bells connected, but ringing voltage can actually exceed 90V.
The electrical outlets in your home pack a whopping 15 amps; your humble telephone carries less than a tenth of a milliamp.
Well, I'll skip over the 15A angle as we all know that the current that actually flows depends upon the resistance.
But the second statement there is just untrue. The standing DC current when a phone is off-hook can be over 100mA. The ringing voltage can certainly pack a similarly dangerous level of current to someone immersed in water.
So let's put it this way: If I was soaking in the tub I wouldn't want anyone to come along a drop a phone in there with me.....