Does possession of the phone prove authorship of its messages?¶

No. Possession supports access and opportunity; authorship requires evidence that the person composed, approved or triggered the particular communication.

Separate the links¶

Ask who possessed the handset, which account held the message, which client submitted it and who produced the words. A local draft, handset-created attachment, keyboard or app-use record can support composition. Provider sessions may instead identify a linked computer, another phone, automation or compromise.

Test the human attribution¶

Content, knowledge, style and later conduct may corroborate authorship but are rarely exclusive. Consider access by others and whether an alternative user fits the time and whole sequence. Secure possession plus local creation traces can make a vague alternative unrealistic without turning possession alone into proof.