You can add them to the Global address list, so that they are visible for anyone with an Exchange Online mailbox. However, this requires admin permissions, regular users cannot create org-wide contacts.
An alternative might be to create them as contacts in your own (custom) Contact list, then share the list with select users/groups. This gives you control over which contacts appear, their contact info and who gets to see them, however the process of "accessing" the list in more involved.
Similarly, you can use a Contact list within a shared mailbox, a Public folder or a SharePoint site. Or "modern" endpoints, such as Microsoft Lists or Loop. Each method has its own pros/cons...
