I looked up the spreadsheet: 1.8GHZ DECT phones are known to cause intereference on two streams, 5 (which has Four) and 11 (which has Prime). The weird thing is that the stream that the interference affects depends on the LNB type (10750 or 11300) so you shouldn't be getting interference on both. My guess is that you have a dual throat, single output 10750 LNB for your MySKY. It's possible that this is failing and causing problems on the other stream. SKY now has quad output LNBs on 11300 to help deal with the interference problem where we can't do a decoder swap. Also you could move your DECT phone as far away from the STB as possible.
A couple of questions,
Does your spreadsheet also have other lnb frequencies listed? I'm pretty sure that my Dad has one which is 10600 (it's a fairly old sky install) and am wondering if this will be listed in the spreadsheet. Do you have a record of what lnb is in use at an address?
Are all of the quad output lnbs 11300, or, are these special ones to get around interference in special cases?