Follow the below mentioned steps to upgrade from R12.2.2 to R12.2.3

Database Tier
Step 1 - Download and Apply following patches (if you are on StartCD 12.2.0.46):

1. 13001379, 16924879, 16929165, 16992075, 17047617, 17461865, 17468141, 17502060, 17184721

Step 2 - Dowload and run Patch for Database Patch Checker (highly recommended) to find out the exact patches you must apply (based on your currently db verstion) to upgrade to R12.2.3 - 17537119

1. Patches recommended by Database Patch Checker - 16187992, 16505333, 17421340
2. In my case, I found that the following patches recommended by DB Patch Checker couldn't be applied on Linux x86-64 as they were Exadata specific - 16101465, 16710753
3. In my case I couldn't find this patches recommended by DB Patch Checker - 16864048

Application Tier
Step 3 - Download and apply following Application Tier patches (if you are on StartCD 12.2.0.46)

1. 8300196, 14703419, 16207165, 16241466, 16271876, 16778382, 17303472

Step 4 - Web Tier and Utilities (OHS) 11.1.1.6 Patches and Bug Numbers - 17325559
Step 5 - Oracle Fusion Middleware Common 11.1.1.6 Patches and Bug Numbers – 12714567 (I had an issue in applying that it wouldn’t accept valid JRE and JDK paths – looks like a bug)
Step 6 - Oracle Weblogic Server 10.3.6.0 Patch and Bug Numbers – I had to play around with Weblogic Smart Update installer (in terms of uninstalling conflicting patches) since there were a number of dependencies and conflicts with already installed patches. Anyways, you must apply the following patches:

1. 13729611, 16083651,
2. 17495356 (not in StartCD)

Step 7 - Apply Consolidated Seed Table Upgrade Patch (Required)

1. If you haven't already applied Consolidated Seed Table Upgrade Patch 17204589 (17204589:12.2.0), then you must first apply Patch 17204589 (17204589:12.2.0) on the Run File System following the below instructions before proceeding with the next steps.
2. If you have upgraded to Release 12.2.0 using Consolidated Upgrade Patch 17197281 [17197281:12.2.0 (CUP4)], then you can skip this step.

Step 8 - Apply the 12.2.3 AD and TXK Release Update Packs

1. If you are upgrading from Release 11i, 12.0.x, or 12.1.x to Release 12.2.3 and have already applied the latest AD and TXK Release Update Packs (the same or higher release version than mentioned in this readme), you can skip this section. The minimum required release versions for AD and TXK upgrading to Release 12.2.3 are R12.AD.C.Delta.3 and R12.TXK.C.Delta.3. 
2. To apply the Release 12.2.3 AD and TXK Release Update Packs, see Document 1586217.1, Applying the Release 12.2.3 AD and TXK Release Update Packs.

Step 9 - Apply the 12.2.3 Suite-Wide Release Update Pack and associated help patch:

1. Apply Oracle E-Business Suite Release 12.2.3 Patch 17020683, and
2. Oracle E-Business Suite Release 12.2.3 Online Help Patch 17020685

Step 10 - Run post upgrade steps of synchronizing the Patch and Run file systems using the command shown below:

adop phase=fs_clone workers=64

References - Database Tier
Oracle Support Document ID 1594274.1, Oracle E-Business Suite Release 12.2: Consolidated List of Patches and Technology Bug Fixes

References - Application Tier
Oracle Support Document ID 1586217.1, Applying the Release 12.2.3 AD and TXK Release Update Packs.
Oracle Support Document ID 1586214.1, Oracle E-Business Suite Release 12.2.3 Readme