Maling List

By submitting this form and signing up for texts, you consent to receive marketing text messages (e.g. promos, cart reminders) from Making Tracks at the number provided, including messages sent by autodialer. Consent is not a condition of purchase. Msg & data rates may apply. Msg frequency varies. Unsubscribe at any time by replying STOP or clicking the unsubscribe link (where available). Privacy Policy & Terms.

You should put the disclosure language above the SMS consent checkbox or button. That way, people see the disclosure language before they opt in. 
Multi-step forms are the best option for collecting both email and SMS consent because they allow you to collect SMS consent separately from email consent. 

Single-step forms are a potential compliance issue, as it may appear you are forcing the customer to sign up for SMS in order to access email marketing. Thus, they are not recommended. 
Word on the street says

we’re pretty darn good at what we do.