Open the Steam app on your phone
Sign in to your Steam account
Go to the game’s store page
Check whether the game is eligible for gifting
Tap Buy or Add to Cart
Select Buy as a gift
Choose a friend from your Steam friends list
Add a gift message if you want
Choose the delivery date if available
Complete the payment
Confirm the gift purchase
If the Steam app does not show gifting options, use your phone browser and sign in to Steam Store
If gifting is still unavailable, use a desktop browser or the Steam desktop client