Is it considered a sin not to pick up a phone found in the street and guide its owner to it, despite the intention of doing good?

There is no sin upon you for not picking up a lost item (Luqatah), according to the majority of scholars. The disagreement lies in the liability of someone who picks up a lost item and then returns it to its original place. Some scholars believe there is no liability upon him if he took it to safeguard it, while others hold him liable because it is a trust in his hand. Since the incident has already occurred, we do not obligate you to guarantee the mobile phone, but we advise you to be mindful of this in the future.