Does the phone emit radiation when wifi is off?

Yes, as you do not specify what type of "radiation".

Anything that mentions radiation without saying what type is a scam or someone that has no clue what they are talking about.

The harmful type of radiation is Ionising radiation - aka Nuclear or Atomic radiation.

Phones and consumer electronics do not emit that.

Phones emit radio waves, light, infra-red - all type of EM radiation - and acoustic radiation; sound.

You own body emits IR and acoustic radiation. Light bulbs emit more EM radiation than phones, power-wise.

[Radiation - to radiate - just means _something_ spreading from a point. eg. Ripples radiate from where you drop a pebble in water. Without saying what is being spread, it's a meaningless word.]

Phones don't emit radiation if they switched off or in airplane mode.  When you are connected by wifi, bluetooth or the telephone network, it emits radiation.