When you select a keyword to filter on, Kibana tries to give you a list of keywords to select from and then creates a query to match phrase. Apparently you can still edit it and add a wildcard.
But according to this page, (go to the very bottom of the page in the box) you can't use wildcards in a phrase match query.
Actually, you can use wildcards but they're either ignored completely or they are trying to match the literal string
123456* with an asterisk in it.
Compare that with the query you get if you put the query in the query bar;
So you could edit the filter and change from the phase query to a regular query so that wildcards are used.