My 82 Year Old Mom Had A Stroke 5 Months

My 82 year old mom had a stroke 5 months ago and they just added amlodipine to her other medications. The phlegm is so thick now that she keeps choking on it and is scaring her. Is this a normal side effect and is there something else she can try to stop the phlegm. We have tried roditussm DM and allergy meds but they are not working.