What is the ruling on benefiting from knowledge acquired through a gifted phone, when it was later discovered that the source of its price was unlawful?

There is no harm in benefiting from what was learned or participated in via a phone purchased with ill-gotten money, especially since the beneficiary was unaware of it. Using usurped money out of ignorance incurs no sin. As for the phone itself, after learning that its money is illicit, it is not forbidden to keep it and benefit from it. The sister should be advised to free herself from the ill-gotten money, for the right is attached to the original buyer's liability, and the money has lost its physical form through the purchase. There is no sin upon whoever receives the item thereafter, as long as they were not complicit in the usurpation.