Collecting users phone number in newsletter signup

[OneDoBit]

Hey!
I would like to add functionality to my newsletter sign-up for people to either sign up by email or phone

I have email input looking like this

<input class="signup-input inline-list" type="email" name="contact[email]" id="email" placeholder="{{ 'password.form.placeholder' | t }}" required>

But what should be the code to have people sign up by phone?

I tried 

name="contact[phone]"

But it didn't work