
Quoting
cdwjava
Here is the law as linked by RJR earlier:
705.102 Reporting lost or abandoned property.—
(1) Whenever any person finds any lost or abandoned property, such person shall report the description and location of the property to a law enforcement officer.
(2) The law enforcement officer taking the report shall ascertain whether the person reporting the property wishes to make a claim to it if the rightful owner cannot be identified or located. If the person does wish to make such claim, he or she shall deposit with the law enforcement agency a reasonable sum sufficient to cover the agency’s cost for transportation, storage, and publication of notice. This sum shall be reimbursed to the finder by the rightful owner should he or she identify and reclaim the property.
(3) It is unlawful for any person who finds any lost or abandoned property to appropriate the same to his or her own use or to refuse to deliver the same when required.
(4) Any person who unlawfully appropriates such lost or abandoned property to his or her own use or refuses to deliver such property when required commits theft as defined in s. 812.014, punishable as provided in s. 775.082, s. 775.083, or s. 775.084.
If the OP wants to remain out of trouble, he should turn the phone over to local law enforcement with the owner's information. The OP's refusal to return the phone would appear to constitute theft per the statute, if that is what he did. Compensation does not appear to be covered in the statute, and to make such a demand in order to fulfill a legal requirement might also be construed as extortion. The OP should just turn the phone over to law enforcement with the owner's info as required per the statute. Easy and done.