On 1 October 2020, a Boeing 787-9 was approaching the top of descent when the cabin crew discovered a mobile phone crushed in a flat bed seat which had just been changed to the seated position for landing. A fire which had started was extinguished and the Captain declared a ‘PAN’ to ensure the fire service attended the arrival. The Investigation noted that there are currently no seat design requirements to prevent electronic devices from becoming trapped in seats and that it is proving challenging to find a workable solution. A Safety Recommendation to improve seat design regulations was made.