One conversation can be enough in some cases, but the key is whether the consultant actually has enough information to recommend you credibly.

A strong consulting referral is about advocacy, not simply obtaining an employee name in the system.

If you ask, make it easy for them to decline: 'If you feel comfortable based on our conversation, would you be open to referring me?' That is much better than assuming the referral is owed because they took the call.

The 'if you feel comfortable' wording is exactly what I used.

If the chat was genuinely good, asking once is fine.