No, it is not safe to use a microwave if you have placed your phone inside, regardless of whether the phone turns off or not. Microwaving a phone can cause serious damage to both the phone and the microwave, and it can also pose safety hazards.
Microwaves emit electromagnetic radiation at a specific frequency that is absorbed by water, fats, and sugars in food, causing them to heat up. Electronic devices like phones are not designed to withstand this type of radiation, and subjecting them to microwave radiation can result in irreversible damage to the internal components.
Even if the phone appears to be turned off or non-functional after being microwaved, it is still not safe to use the microwave. Microwaving a phone can cause the battery to overheat and potentially explode or catch fire, which can lead to a dangerous situation.
If you accidentally microwaved your phone, it is best to avoid using the microwave until it has been thoroughly cleaned and inspected by a professional. Additionally, do not attempt to use the phone again, as it is likely damaged beyond repair and may pose safety risks.