What is today's version of the 'cutting the phone line' trope?

The old Cut Phone Lines trope has been replaced with the Cell Phones Are Useless trope. It really requires no more thought than any Cut Phone Lines, you just have to have cut the power (to avoid being able to recharge) and have the cell phone battery die.

This isn't difficult to imagine; I still have an iPhone4 and that battery barely lasts 10 hours with no usage, and at most 3 hours if I'm texting/Facebooking. If I'm in a house babysitting and I forget to recharge, I'm basically serial killer bait by 10PM.

The "phones are dead" trope is still very much a part of story telling but usually appears only in some area effect context (usually with explosions and someone looking constipated or throwing an oh-mah-gawd-we're-in-the-sticks eye roll).

I assume you are not referring to that general case but asking how one party could prevent another adversary from making a phone call in the modern age, and there are two ways: take the device or take the connection.

Your bad guys could "cut the phone line" by either taking out the local cell phone towers or deploying a jamming device (or both).

Cell phone jammers are obtainable/manufacturable but have been illegal in the US since the beginnings of the technology so there aren't a lot of Action McNews stories about them, which is where writers absorb ideas from.

I think that's why jammers are not more common in stories.