Virtually nobody has landlines nowadays.
Like
@SouthAussie mentioned, police aren't allowed to be present whilst Erin is speaking to lawyers, that conversation is privileged.
But also, police aren't allowed (before a suspect is charged) to accompany them to a bathroom, either.
It doesn't point to police incompetence, IMO.
The fact she changed the sim while the police were in her vicinity, and then, factory reset the phone remotely when the phone was in police custody, is damning evidence IMO.
None of this "doubt" raised by Mr Mandy SC is very compelling, IMO