You are downloading the BT OnePhone AppX file v126.96.36.199 for Windows Phone. BT OnePhone is a free and useful Productivity app: BT One Phone brings your fixed lines, mobile phones and phone system ... You can now download the offline AppX file to install & try it.
Download Locations for BT OnePhone 188.8.131.52 AppX file
Important Notice: Now Due To Unspecified Limitations, You Can Not Use The Offline AppX File To Install It Any More.
To try to install it manually from an SD card, you should choose one of the server location above to get the offline BT OnePhone AppX file, move the file to your phone's SD card and then tap 'Install local apps' in the phone's App list.