From the Heathrow Airport site, try
https://www.heathrow.com/at-the-airp.../lost-property
(I left my phone in a rush through security to make a connection, it took a little over a week for a match on the database. I'm not sure how long lost property will be kept here before disposal*).
*Edit to add, page says three months from arrival at the lost property office - so check as soon as possible!