Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Call emergency services for speech difficulty that begins suddenly, especially with facial drooping, weakness, severe headache, confusion, loss of balance, or difficulty understanding speech.
Seek prompt medical assessment if a child loses speech or language skills they previously had.
Loss of skills is not a typical feature of an uncomplicated phonological disorder and may have another cause.
In any child or adult, these may be signs of a stroke or another urgent neurological problem.
Sudden speech change after a head injury, choking episode, or breathing problem also needs urgent care.
Arrange a routine assessment if a child’s speech is regularly difficult to understand, sound errors are causing frustration, or the child avoids speaking.
It is also reasonable to seek advice if speech seems to be progressing more slowly than expected, errors persist, or a teacher raises concerns.
The article also says
Ask about a hearing evaluation if the child often does not respond to sounds, turns up devices unusually loudly, has repeated ear problems, or has not had hearing checked.
Every sign above is quoted from the sofidex article on Phonological disorder. If you are not sure, err upward — it is always reasonable to be checked.