Short answer
HubSpot's KB: on iOS and Android you can reply to open conversations and add comments for teammates. Filter by status, channel, contact, assignee or date. Only legacy knowledge base articles can be shared from the mobile inbox.
1. In HubSpot
The relevant screen in my demo portal.

2. Worth knowing
Set mobile notifications so chats aren't missed away from a desk.
3. Related
Inbox channels and mobile calls.