Google Search ads show on phones, tablets and computers. To bid more or less on phones, open "Ad schedule, devices and dates" in section C of the Google Search campaign.
To show in Gmail, on YouTube and in the Discover feed on phones, add Google Gmail, YouTube & Display: press Add Gmail, YouTube & Display at the top of the Google Search campaign, or tick it in step 2, Where it runs. The same brief writes its text, and its pictures come from your ads.