Suppliers of cordless phones advise in their instruction booklets that these are not to be relied upon for emergency calls.
The preponderance of personal & works mobile phones these days would suggest this shouldn't be an issue though?

While looking at phones, bear in mind that office phones (cordless or otherwise) are often routed via a switchboard system and if that loses power, you may not have any phones at all.

As stated, probably not an issue in view of mobiles being available.

We have a VOIP system, which goes down in a power cut or a network outage. For emergency use we have a small number of red telephones in prominent places, which are BT lines and are connected to a dedicated BT line at reception. The accessible emergency phones have only two buttons, one for Reception (daytime) and one for Security (night time). We do not rely on mobiles for emergency use, as we need a means of communication that goes to a well identified muster point (reception) where messages can be handled and passed on.