| Document and Entity Information | Apr. 16, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Apr. 16, 2021 |
| Entity Registrant Name | PHX MINERALS INC. |
| Entity Central Index Key | 0000315131 |
| Entity Emerging Growth Company | false |
| Entity File Number | 001-31759 |
| Entity Incorporation, State or Country Code | OK |
| Entity Tax Identification Number | 73-1055775 |
| Entity Address, Address Line One | 1601 NW Expressway |
| Entity Address, Address Line Two | Suite 1100 |
| Entity Address, City or Town | Oklahoma City |
| Entity Address, State or Province | OK |
| Entity Address, Postal Zip Code | 73118 |
| City Area Code | 405 |
| Local Phone Number | 948-1560 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of each class | Class A Common Stock, $0.01666 par value |
| Trading Symbol(s) | PHX |
| Name of each exchange on which registered | NYSE |
