I'm curious to see what will happen with LTE-M in this context. Is it going to be phased out as well?

According to Ericsson: > Cat-M1 and NB-IoT are considered future-proof and are viewed as 5G technologies

But AFAIK Cat-M1 falls into the "LTE" umbrella, which means it could be phased out by T-Mobile

Agreed. These technologies are the backbone of a lot (most?) of IoT devices, so unlike the article's description of "devices" in terms of "consumer handheld phones (that are often replaced every 3 years)", the impact here would be much deeper. And these technologies have been and are continuing to be sold as stable. For example, see https://www.nordicsemi.com/Products/Wireless/Low-power-cellu... . Quote: "Future-proof: LTE-M and NB-IoT are slated for support beyond 2040, ensuring devices' long lifespans. Subscriptions guarantee a reliable network, in contrast to other LPWANs that could shut down preemptively, risking your business." On the other hand, I guess I haven't seen as many IoT devices choose T-Mobile as a carrier either, so maybe it's just that T-Mobile knows their market.

>The document goes on to mention that T-Mobile will retain a small 5 MHz-wide channel of LTE across the country. This will be maintained until at least 2035 to accommodate legacy IOT devices, which can range from ATMs to smart infotainment systems in vehicles.

Your old phones are safe for now

Pretty wild something called "Long Term Evolution" is being phased out

Well atleast they will keep some of it going. Where I live 5G is pretty much worthless and might as well not exist for all the service it provides.