The son has phlegm in his throat, which makes him hoarse - can I additionally use e.g. Hederasal or Mucosolvan inhalations?

Inhalations can be used - in this case after consulting a doctor, since Mucosolvan inhalations are available by prescription. You can also use concentrated salt for inhalation, e.g. Marimer inhalation 2.2%, which dilutes the residual secretion and makes it easier to get rid of it. I do not know what age your son is - it may be worth considering the implementation of an appropriate syrup with expectorant effects, according to the age of the child (eg ACC, which also supports the thinning of secretions). The above drugs should be used during the day, until 17 o'clock. Below you will find information about the listed preparations: https://www.gdziepolek.pl/produkty/90688/acc-classic-plyn/apteki https://www.gdziepolek.pl/produkty/95861/marimer-inhalation-plyn/apteki https://www.gdziepolek.pl/produkty/50563/mucosolvan-inhalacje-plyn/apteki