[Bug] The Get Code button is disabled on Trial Registration Page

Summary

Users could not click on the Get Code button after input correct phone number.

Steps to reproduce

1. Visit free trial registration link
2. Input a phone number
3. The Get Code button should be clickable, not grey.

Example Project

What is the current bug behavior?

The Get Code button is grey.

What is the expected correct behavior?

The Get code button should be clickable.

Relevant logs and/or screenshots

Output of checks

Results of GitLab environment info

Expand for output related to GitLab environment info

(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)

(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)

Results of GitLab application Check

Expand for output related to the GitLab application check

(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:check SANITIZE=true)
(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)
(we will only investigate if the tests are passing)

Possible fixes