I Have studied Line CSS has more precedence than Device CSS, Line CSS is for blocking pattern where as Device CSS can be used for Routing pattern.
For Ex
Line CSS has blocked partitions
Partition---- International
Partition--LD
Device CSS has partition
Local
International
LD
If IP phone contain both device and Line CSS , it can not be able to call international and LD as line CSS is blocking those partitions.
Please correct me if I am wrong?
https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/srnd/8x/uc8x/dialplan.html#wp1150997
Yes, as per your example, the IP Phone won't be able to dial LD and International Numbers because both Line and Device CSS contains LD and International Partition. The Phone is able to dial Local Numbers only.
You may find this useful:
https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/srnd/collab12/collab12/dialplan.html#39529
G