Watsapp

 The articles I’ve read on this simply quote the Government as saying: They don’t have it and Boris  had not handed it over IN TIME to safely download the data and hand it in to the Inquiry

That says to me the phone is with whoever is safely downloading the data - aka security services - or the Government would’ve simply said Boris hasn’t handed in the phone. 

Also worth noting that Lady Hallet hasn’t to my knowledge issued more legal proceedings or gone public saying he hasn’t been cooperating.