I think you've conflated SEVERAL things here which should be decoupled.

1. Getting NOs from investors is NEVER EVER EVER good. I cannot stress this enough. Each no you get will compound the likelihood you do not ultimately raise.

2. You should not be worried about others stealing your idea because execution is the only thing that matters. HOWEVER there is a big difference between pitching a novel concept without any social cohesion and just throwing it to the wind and seeing what sticks.

3. All practice sessions for fundraising pitches MUST be done with friendlies so that you can adjust the pitch and then keep it consistent in public.

4. Phone sessions are radically different than slide sessions and require a specific set of strategies to succeed.

This is not to say that you cannot fundraise from a lack of experience. But rather, raising money is JUST LIKE auditioning for a part. You only have one chance to make a first impression.

Don't blow it.