can I say, "mobile phones are thought to be bad for our health"?

See a translation

You can say this - it’s fine.
In fact you can read similar statements in magazines and elsewhere.

“Mobile phones are thought to be bad for our health.”

People have different ideas about the problems these phones cause-
from issues with our brains, to mental health and social issues from being on the phone too much,
to physical problems that people can have with their eyesight, hands, and yes posture.
People can get themselves killed by texting while driving.
The list is endless and goes on and on and on.

Some of the problems are clear. Some are unclear and unstudied.

So- yes the sentence is fine and you can say this.