diff --git a/artifacts/CAMARA_common.yaml b/artifacts/CAMARA_common.yaml
index fdbeede8..2096bcd7 100644
--- a/artifacts/CAMARA_common.yaml
+++ b/artifacts/CAMARA_common.yaml
@@ -61,10 +61,10 @@ components:
    minProperties: 1
 
   PhoneNumber:
-   description: A public identifier addressing a telephone subscription. In mobile networks it corresponds to the MSISDN (Mobile Station International Subscriber Directory Number). In order to be globally unique it has to be formatted in international format, according to E.164 standard, optionally prefixed with '+'.
+   description: A public identifier addressing a telephone subscription. In mobile networks it corresponds to the MSISDN (Mobile Station International Subscriber Directory Number). In order to be globally unique it has to be formatted in international format, according to E.164 standard, prefixed with '+'.
    type: string
-   pattern: '^\+?[0-9]{5,15}$'
-   example: "123456789"
+   pattern: '^\+[1-9][0-9]{4,14}$'
+   example: "+123456789"
 
   NetworkAccessIdentifier:
    description: A public identifier addressing a subscription in a mobile network. In 3GPP terminology, it corresponds to the GPSI formatted with the External Identifier ({Local Identifier}@{Domain Identifier}). Unlike the telephone number, the network access identifier is not subjected to portability ruling in force, and is individually managed by each operator.
diff --git a/documentation/API-design-guidelines.md b/documentation/API-design-guidelines.md
index 1a0a402a..5d02e9d1 100644
--- a/documentation/API-design-guidelines.md
+++ b/documentation/API-design-guidelines.md
@@ -1551,7 +1551,7 @@ curl -X 'POST' \
   "data": {
     "subscriptionId": "456g899g",
     "device": {
-      "phoneNumber": 123456789
+      "phoneNumber": "+123456789"
     },
     "roaming": true,
     "countryCode": 208,
@@ -1588,7 +1588,7 @@ curl -X 'POST' \
   "data": {
     "subscriptionId": "456g899g",
     "device": {
-      "phoneNumber": 123456789
+      "phoneNumber": "+123456789"
     },
     "terminationReason": "SUBSCRIPTION_EXPIRED"
   },
diff --git a/documentation/Glossary.md b/documentation/Glossary.md
index 37d06a04..9eabab44 100644
--- a/documentation/Glossary.md
+++ b/documentation/Glossary.md
@@ -5,7 +5,7 @@
 | ------------ | ----------- | ----------- |  ----------- |
 | **Device** |End-user equipment able to connect to a network. Examples of devices include smartphones, home gateways or IoT sensors/actuators.  | device |  |  |
 | **Application Server** | A server hosting backend applications to deliver some business logic to clients. | applicationServer |  |  |
-| **Phone Number** |A public identifier addressing a telephone subscription. In mobile networks it corresponds to the MSISDN (Mobile Station International Subscriber Directory Number). In order to be globally unique it has to be formatted in international format, according to E.164 standard.  | phoneNumber |  |  |
+| **Phone Number** |A public identifier addressing a telephone subscription. In mobile networks it corresponds to the MSISDN (Mobile Station International Subscriber Directory Number). In order to be globally unique it has to be formatted in international format, according to E.164 standard, prefixed with '+'.  | phoneNumber |  |  |
 | **Network Access Identifier** |  A public identifier addressing a subscription in a network, defined in [IETF RFC 7542](https://datatracker.ietf.org/doc/rfc7542/). In 3GPP mobile networks one such option is the General Public Subscriber Identifier (GPSI) formatted with the "External Identifier" as ({Local Identifier}@{Domain Identifier}). Unlike the phone number, the network access identifier is not subjected to portability ruling in force, and is individually managed by each operator. | networkAccessIdentifier  |  |  |
 | **IP v4 Address** | Identifier of a node in a network using Internet Protocol version 4 (IPv4). IPv4 uses 32-bit addresses, which are insufficient to allocate unique addresses to all current devices. In order to mitigate this, network operators use Network Address Translation (NAT), mapping a private IP address space to a public one. | ipv4Address |  |  |
 | **IP v6 Address** |  | ipv6Address |  |  |  |  |