Is refraining from visiting a mother who practices sorcery, attempts to harm her children, and has caused family problems considered a severance of kinship ties? And is merely communicating with her via phone considered maintaining kinship ties in this situation?

If the mother's misconduct is established, one must be patient with her and frequently supplicate for her guidance, and beware of mistreating her, for honoring one's parents is obligatory even if they wrong you. If there is fear of her harm, then cutting ties with her is not considered an act of disobedience, but one must maintain a connection with her in any possible way, such as by calling. One must continue to advise her with gentleness and kindness, and seek out someone who might influence her towards guidance.