Quran 2:183 Prescription Of Fasting
There is not context to lead us to think otherwise that the few days are not the day of Ramdan. The reason here to call the full month as a few days, is to encourage the audience to keep fast for this small period. We use this expression in our language too to make a somewhat longer period as shorter to make it less tedious. Moreover, the ruling of make up fasting in other days if missed during the prescribed days for some reason, rules out possibility of any other fast, because no other fasting is mandatory. for such a context, when preceding and following verses are dealing with the same topic, an exception needs to be well defined, which is not the case here.