You basically have two choices. You can set up a lookup chart and use VLOOKUP to find the number and its corresponding text, or you can use a formula like IFS to list the possibilities individually. Which one you use is probably most affected by the number of combinations you have to include. Also, if there is any likelihood that the data would change and need editing, the chart and VLOOKUP option will make that easier.
Chart and VLOOKUP:
In the screenshot the sample chart is in F1:G6. The formula used in B2 and filled down is:
=VLOOKUP(A2,$F$2:$G$6,2,FALSE)

IFS formula with choices included in the formula:
In the screenshot this formula is in C2 and filled down:
=IFS(A2=1,"Small",A2=2,"Medium",A2=3,"Large",A2=4,"X-Large",A2=5,"XX-Large")
