What is the ruling regarding a telephone found inside used furniture purchased from the Zakat committee, knowing that its owner cannot be identified?

The phone found inside the set you purchased is considered a lost item (Luqatah), not your property. It must be announced for a year in public places, or handed over to the competent authority.

If the seller of the set claims ownership of the phone, his claim is to be believed. However, if he denies ownership, then the phone must be announced as a lost item, and you are permitted to appoint someone to make the announcement on your behalf.

After one year of announcing it, you have the option to keep the phone (without guarantee if it breaks), or to benefit from it, or to give it away as charity. If its owner appears after that, he is given the choice between the value of the phone or the reward of the charity.