As grateful as he was that Rose was not in danger yet, he was also angry at himself for making the Master aware of his presence. Hopefully he wouldn't get to her before the Doctor escaped; if anything the sound of the Master made him even more determined not to die.
Leave her out of it.
But who else did he know in L.A? Perhaps he had been referring to Romana, but the Doctor at least knew Romana had the strength of mind to hold her own. As much as he hated to ask for any assistance from the Master he just had to ask. Where is Romana?