Bear with me folks, cos this isn't my problem. ( Yet. It soon will be though. )
Scenario: Bungalow with router inside. Portakabin with business computer and telephone twenty yards or so across the yard. Until the last storm, a cable joined up the two without too many problems. When the wall holding up the post holding the cable fell down, connection was lost. As was a section of wall, half the post, an electric cable and a few yards of phone cable.

Customer says, can I find some heavier duty outdoor type phone cable, and refit it? Can't we do it wirelessly, say I ? Right, here are the present problems, and the stipulations.
Apparently, the existing router can't send a strong enough signal across the yard for the existing kit to work*. Will something like this and
assuming they haven't already got something similar in there, this work?

My other thought was a range extender to boost the signal from the bungalow.

The main worry my customer has is whether a wireless link will be as secure as a hard wire. She uses it for business, and doesn't want any Herbert who comes into the yard picking up her details on their smartphone/ipad. I think that as long as the router is password protected, she'll be OK, but I'd like your views on this.
The other stipulation is that they must have a phone in there as well, so will these wireless efforts send a phone signal as well? If they didn't want internet access, a cordless phone would have solved the problem, but I wouldn't like to tell them they have to buy two separate items to get phone and internet across the yard.

* My old Livebox sends a signal at least a hundred yards, cos I've driven off in the van, and seen how far I got before I was out of range. Theirs seems very poor.

The items I've linked to are simply for illustrative purposes. The first ones I came across.
Thanks in advance folks, as always.