Cardstock like a business card is heavier and more durable than paper. Some people keep business card albums (like a photo or baseball card album with individual pockets in the sleeves for each card). It helps keep all business cards in one place, like a rolodex.
Puting the info in your phone is a good idea, but sometimes, things happen to phones. Contacts get lost (seen it happen), phones die, phones get lost, etc. Having a back up is a good idea.
By the way, your SS card is more than printer paper. It's heavier duty. Your DD214 is not carried with you all the time I imagine. Probably kept safe somewhere as is mine.
Having different options is always good.