Usually. You can check by putting your phone in and closing the door while looking at the signal strength meter. It should go without saying don’t turn the microwave oven on with your expensive electronics inside. If you get decent reception in the closed oven, you need a new one.

Definitely works to kill reception forever if you power up the microwave for a couple of minutes…

"you need a new one." <-- New microwave, I presume?

You may just need to clean the inside of the door so it closes better. Try that first.

They did quite well for 3G and even 4G which didn't have as many above 2.4GHz , but after 4GLTE, 5G has added a lot of mid-bands between 2.6-6GHz. Those tend to leak more since they have shorter wavelengths than microwaves are built around 2.4GHz. Some of them are only used in a few countries, but n2 & n77 are widely used by ATT.

https://en.wikipedia.org/wiki/LTE_frequency_bands

https://en.wikipedia.org/wiki/5G_NR_frequency_bands

You gotta take that phone out sometime though to heat up your ramen.

4GLTE/5G compatible microwave is needed!