Why a campaign is always outbound
There is no direction control, because a campaign that waits for the phone to ring is just a channel.
Every campaign is outbound and there is no setting to change that. It is worth understanding why, because the reasoning explains how the whole product is divided.
A channel is a line something arrives on. A campaign is a list you work through. A campaign that waited for the phone to ring would have no list and no sequence — it would just be a channel with extra words.

Reference
Notice there is no direction setting
The control does not exist because there is nothing to choose.
This is worth understanding rather than working around. If you find yourself wanting an inbound campaign, what you want is a channel with incoming enabled, pointed at a bot or a call flow.
Use a channel for inbound
A channel with incoming enabled, pointed at a bot or a call flow. That is what "handling inbound calls" is.
Use a campaign for reaching out
A list, a sequence and a line. Those three things are what a campaign is, and none of them makes sense for a call you did not initiate.
The two halves meet on the contact record: a channel captures and qualifies, a campaign picks up everybody at that stage and calls them.
Combine them for a real process
An inbound enquiry is answered by a bot, qualified, and its stage moves. A campaign then picks up everyone at that stage and calls them. The two halves meet on the contact record rather than in an integration.
Notice the campaign list reflects this
It shows "Answers with" rather than a Type column, because the type would say the same thing on every row.
Put it to use
Build the pair once: a channel that captures and qualifies, and a campaign whose audience is a filter on the stage that channel produces. That is the shape most teams end up with, and it is worth arriving at deliberately.
The parts people get wrong
- A call flow used by a campaign needs Runs on set to the autodialler rather than to incoming calls.
- An inbound-only SIP gateway will never appear in a campaign's line picker, for the same reason.