Answered by Ustadh Tabraze Azam
Question: Assalamu alaykum,
In a previous fast I felt I had swallow water which mixed with phlegm at the back of my throat. I was not able to cough it up. Does this mean my fast was invalid?
Answer: Wa alaikum assalam wa rahmatullahi wa barakatuh,
I pray that you are in the best of health and faith, insha’Allah.
Ignore it. If you rinse your mouth during the fast and then spit out, the remnants of the water in the mouth are of no consequence.
And expiations (kaffara) are only due for deliberately corrupting Ramadan fasts.
Please see: A Ramadan Reader: A Comprehensive Answers Guide to Getting the Most Out of Ramadan and: The Complete Guide to Fasting and Ramadan
And Allah alone gives success.
Checked & Approved by Faraz Rabbani