I have Cisco 8861 phone, how to configure this for Asterisk:
Load: - sip88xx.11-7-1-17
sip88xx.11-7-1-17 are for Enterprise phones. You should be using MPP (3PCC) phones if you want to register to Asterisk. I would suggest getting it replaced with the right SKU.
You can find the right model here: https://www.cisco.com/c/en/us/products/collateral/collaboration-endpoints/unified-ip-phone-8800-series/datasheet-c78-738030.html?cachemode=refresh
Look for Table 5 under Ordering Information.