Multiple Match Phrase Prefixes Return Zero Results In Elasticsearch - elasticsearch

Question

I have the following Elasticsearch, version 2.3, query which produces zero results.
{
"query": {
"bool": {
"must": [
{
"match_phrase_prefix": {
"phone": "123"
}
},
{
"match_phrase_prefix": {
"firstname": "First"
}
}
]
}
}
}
Output from above query:
{
"took": 3,
"timed_out": false,
"_shards": {
"total": 1,
"successful": 1,
"failed": 0
},
"hits": {
"total": 0,
"max_score": null,
"hits": []
}
}
Output of above query with _explain
{
"_index": "index_name",
"_type": "doc_type",
"_id": "_explain",
"_version": 4,
"_shards": {
"total": 2,
"successful": 1,
"failed": 0
},
"created": false
}
However, when I do either of the following I get results including the one document that matches both parts of the above query. If I include the full phone number then the document will appear in the results.
Phone numbers are stored as strings without any formatting. i.e. "1234567890".
Any reason why the two prefix query returns zero results?
{
"query": {
"bool": {
"must": [
{
"match_phrase_prefix": {
"phone": "123"
}
}
]
}
}
}
{
"query": {
"bool": {
"must": [
{
"match_phrase_prefix": {
"firstname": "First"
}
}
]
}
}
}

Answer 1

I was able to get the results I wanted by changing the phone number query to a regexp query instead of a match_phrase_prefix query.
{
"query": {
"bool": {
"must": [
{
"regexp": {
"phone": "123[0-9]+"
}
},
{
"match_phrase_prefix": {
"firstname": "First"
}
}
]
}
}
}