Modify regex for max length

Question

I'm evaluating a phone number in js with this regex:

/[a-z]/i.test(this.state.phone)

Now I need to limit its length to 30 chars. I tried so many times but basically I know I need to specify max lenght in curly braces like this:

/[a-z]{30}/i.test(this.state.phone)

But this way the check about letters doesn't work anymore. I've spended too much time on it I need some help!

EDIT: to clarify I need to avoid any letter (upper or lowercase) or special char but round brackets, space, dot, minus and plus sign. So this is ok:

+001.333 123456

this not

+001 333 123456v

Answer 1

Now I need to limit its length to 30 chars

/[az]{30}/i will check for exact 30 characters, you need to specify minimum length as well.

/\d{1,30}/i 

{1,30} will check for min 1 and max 30 characters.

Also, if there no other characters allowed in this.state.phone , then asset start of string ^ and end of string $ as well.

/^(\+)?[0-9\s]{1,30}$/