How to Treat a Child’s Sore Throat with Phlegm?

A child, male, 5 years old, has had a fever and cough before, and now although he is almost recovered, he still feels phlegm in his throat and sometimes makes a whistling sound. What should be done? He is currently taking Shuanghuanglian Oral Liquid and Fresh Bamboo Decoction. I would like to ask experts if this medication is appropriate? Are there any better herbal medicine suggestions?
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