Social media and mobile are as tightly linked as highways and cars.
Instagram, Twitter and all messengers are inherently mobile, not just in their design but at their core. Their pattern derive from mobile usage, as opposed to desktop patterns.
Twitter is clearly a byproduct of phones: same length as SMS, even worked through SMS at the start (when smartphones were mostly a cool concept or weird devices). There are tons of sources linking social media and smartphones, see for example https://marketingland.com/facebook-usage-accounts-1-5-minute...