Screen size, typing speed, Microsoft Apps which with VDI are not made for touch screens. In a pinch you can do it but you are not putting in hours. Now a phone docked that Samsung DEX tried maybe but the phone integrations for phone things would need to be there. Its fun but not practical for normal office workers from what I have seen and even with Doctors who wanted it since 2008 still just use it a bit but then on a iPad is another story and works for them perfectly depending on their VDI more than the formfactor.

I've never seen who uses excel be very happy on a phone / tablet form factor... weird stylus workarounds etc... the office apps work best with a keyboard and mouse basically