I have a couple questions to better understand the root cause of your issue.
If the far end cannot hear you then it is typically a NAT issue. Does the phone have a private IP address and is behind a router? That router must have a SIP alg to inspect the packets and replace the private IP address with the public IP address contained in the SIP messaging.
You can confirm this by connecting/configuring a public IP address on your phone and making a test call and confirm 2 way audio.
Second point if the audio is low there are audio gain settings under the phone tab to increase the db level of the sending audio. The gain settings are available for each interface of handset, headset, and speakerphone.
If you look at other products look at the data sheet for SIP alg support.
As for the admin access of the SPA phone, by default there is no password set for admin access. If there is one set, then most likely your phone SIP provider set a password when the configuration was pushed to the phone.
You can contact your SIP provider and ask for configuration change or last option try to factory default the phone and manually configure the SIP settings. How did you configure the device to begin with if you didn't have the admin password.
Configure Multicast Paging on the Cisco IP Phone 7800 Series or 8800 Series Multiplatform Phone
The Cisco IP Phone 7800 and 8800 Series Multiplatform Phones provide voice communication over an Internet Protocol (IP) network...
Add Call Park on a Cisco 7800 or 8800 Series Multiplatform Phone Key Expansion Module
Call park allows the user of the phone to put an incoming call on hold so that the call can be retrieved on another phone. A call is park...