By Agence France-Presse
Hui had grabbed the phone from the woman in the Legislative Council and dashed into the men's toilet. The 36-year-old has since apologised and said he did it because he suspected the government was collecting personal information on lawmakers in breach of the Privacy Ordinance.
Despite his apology, Hui has been denounced by government leaders and lawmakers and even sacked by his own party.
Hui is the latest pro-democracy lawmaker to come under fire after six others were disqualified from the legislature.
Pro-democracy lawmakers denounced his arrest as an overreaction.
"The whole case has been blown (out) of proportion and you can't help thinking that the upcoming prosecution is actually persecution with the aim of ousting of one more democratic member of the local legislature, and this is not acceptable," said legislator Claudia Mo.
She said that if Hui was convicted and sentenced to more than three months' jail he would automatically lose his seat.
Six lawmakers including former protest leaders and independence activists were ousted from the legislature in 2016 for inserting protests into their oaths of office after an intervention by Beijing.
After the disqualifications, the democrats lost their veto power and failed to regain it at by-elections in March.