Me he dejado o He dejado

[BobRitter]

Me he dejado mi teléfono móvil en la oficina.

He dejado mi teléfono móvil en la oficina.

Antosch-and-Lin.com daily phrase uses the first.

The "Me" seems redundant.

[AngelicaDeAlquezar]

It depends on the region. In Spain it's more common to say "me he dejado..." and in Latin America (at least in Mexico) it's more common "he dejado...", or rather simply "dejé..." :D

And if you want to be very Mexican: "se me quedó el teléfono en la oficina" (I didn't leave it there, it just happened) ;)