if I can not find my receipt. still can I sent my iphone to repair?

Some of this information Apple may already have. Go to this web site:

Check Your Service and Support Coverage - Apple Support - https://checkcoverage.apple.com/

If you do need receipts:

For receipts for items from the on-line store go to apple.com, scroll to the bottom, and click on Apple Store Account. --> https://www.apple.com/us/shop/goto/account (only the past 18 months)

For a physical Apple Store purchase you can try contacting the store where you purchased the phone and see if they still have a record of the purchase.

Viewing & Changing Orders - Shopping Help - Apple - https://www.apple.com/shop/help/viewing_changing_orders - "Once an item is shipped or picked up, Apple will create an invoice for your order. To view or print your invoice, go to your Order Listing(Opens in a new window) page and select an item to go to the order details. Then, select View Invoice at the top of your order details page to access your invoice. If you need help viewing or printing your invoice, speak with an Apple Specialist at 1‑800‑MY‑APPLE."

Apple recommends you "Keep your receipt after you buy an Apple device" - https://support.apple.com/HT202711

For questions regarding 'iPhone Screen Repair & Replacement' click here --> https://support.apple.com/iphone/repair/screen-damage

iPad Service and Repair - https://support.apple.com/ipad/repair/service

For the iPad it is unlikely Apple will even offer to repair it:

Obtaining service for your Apple product after an expired warranty [was: Vintage and obsolete products]

https://support.apple.com/HT201624

For the iPhone, any warranty or extended warranty has expired. You will be paying the full repair price and having a receipt shouldn't make any difference. They only really need it if you are claiming warranty service and for some reason a device is not in their system, or you are trying to get an activation lock removed.