Your record for Amy Smith would be right as she married John Smith in 1850 so no other record for the death of Amey Phillips in 1858
Her mother, also Amey Phillips [nee Richards] died 27 Aug 1857
Baner Cymru, Wed Dec 9, 1857 Deaths
Aug 27, at Walton House, Llangollen, age 69, Amy, widow of the late Mr Joseph Phillips, proprietor of the Hand Hotel, Llangollen, for many years.
Probate (16 Mar 1858)
The Will with Codicil of Amey Phillips late of llangollen in the county of Denbighshire deceased who died 27 Aug 1857 at llangollen aforesaid was proved at St Asaph by the oaths of Ebenezer Cooper of Llangollen aforesaid currier and Robert Baker of the same place Maltster the executors.
Given that the census record was taken at a single instant in time, John Smith could have been away - either temporarily on business or visiting, or maybe had returned to Ireland - did he have other children there?
I haven't yet found him locally to Denbighshire or Shropshire