Set single customer in AgentTicketPhone page

[lucasdgr]

I have only a single client on my system otrs.
I want when creating a ticket is set the "from (client)" field in AgentTicketPhone page. Marrow, which is loaded automatically and I have a single client.
In this way the agent has to setear the field.
Similarly to AgentTicketEmail.
is it possible?
please do it as I can?

thanks