Try dissolving in ethanol at slightly higher temperature for a higher time. Hope it works!

Phenol-formaldehyde resin is "like" a one-way street; once formed, it cannot be turned back into the starting points & get additives from it according to our present knowledge. As you know, this thermosetting polymer has 3-D  cross-linked network structure which has many primary covalent bonds which render it insoluble  "in oils & common solvents"& infusible.

There was a question about the P/F resin last year at Research Gate & it is useful to see it plus the comments made by RG colleagues.

https://www.researchgate.net/post/I_would_like_to_ask_how_to_dissolve_phenol-formaldehyde_from_the_surface_of_basalt_wool_I_used_ethanol_at_40C_for_20_min_Is_there_another_method

Can be done - but it depends on what your reinforcement is made up of.  You cannot dissolve the resin away with solvent.  You have to degrade it - typically with an oxidizing solution.

When you want to clean silicon wafers of all residual organic photoresist during microchip manufacturing, the wafers are dipped into "piranha etch" solution: a mixture of sulfuric acid and hydrogen peroxide.  This will oxidize and dissolve pretty much any organic substance.  If your reinforcement is inorganic and not prone to oxidation or acid, this would work.  Piranha etch solutions are a pain, though - dangerous to prepare, dangerous to use - too much organic causes intense bubbling of O2 and H2 (with fire hazards).

If you want to go a little milder, you can try Nochromix, which is not quite as dangerous.  You can order pouches of nochromix from any chemical supplier - or even Amazon.  Nochromix is a different oxidizer (a persulfate salt) dissolved in sulfuric acid.  This is safer to prepare and safer use than piranha.

Hi Sabarinathan

References 1

https://en.wikipedia.org/wiki/Phenol_formaldehyde_resin

2

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0ahUKEwi58dyW_cLWAhWiApoKHRUxBWYQFggwMAI&url=https%3A%2F%2Fweb.anl.gov%2FPCS%2Facsfuel%2Fpreprint%2520archive%2FFiles%2F36_2_ATLANTA_04-91_0664.pdf&usg=AFQjCNEBU33r5IsUIdy3a_jKSynbeJwSpQ

3

https://www.hindawi.com/journals/tswj/2014/940502/

4

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&uact=8&ved=0ahUKEwi58dyW_cLWAhWiApoKHRUxBWYQFgg8MAQ&url=http%3A%2F%2Fwww.springer.com%2Fcda%2Fcontent%2Fdocument%2Fcda_downloaddocument%2F9783319034638-c2.pdf%3FSGWID%3D0-0-45-1500778-p176349961&usg=AFQjCNG-_dg_s9CFMFQoOSjSu2M4bWOywQ

5

https://www.sciencedirect.com/science/article/pii/S1687850716300863

6

https://materialchemistry.com/DreamHC/Download/Phenolic%20Reactions.pdf

7

https://onlinelibrary.wiley.com/doi/10.1002/app.45124/pdf

8

https://www.mdpi.com/2073-4360/8/5/159/pdf

9

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=10&cad=rja&uact=8&ved=0ahUKEwi58dyW_cLWAhWiApoKHRUxBWYQFghaMAk&url=http%3A%2F%2Fwww.mdpi.com%2F2073-4360%2F9%2F8%2F373%2Fpdf&usg=AFQjCNGN8qSLsLMBidfq2P4A16j_YAx0Vg

10

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5554049/

11

https://www.ncsu.edu/bioresources/BioRes_09/BioRes_09_3_4063_Chen_CFQ_Therm_Degradation_Stability_PF_Resin_5492.pdf

12

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=13&cad=rja&uact=8&ved=0ahUKEwifvMD2_cLWAhWGO5oKHaqqDxg4ChAWCDIwAg&url=http%3A%2F%2Fciteseerx.ist.psu.edu%2Fviewdoc%2Fdownload%3Fdoi%3D10.1.1.624.1661%26rep%3Drep1%26type%3Dpdf&usg=AFQjCNHmQSH57wWYrSpuJfIteq0cVg6hlg

13

https://www.novapublishers.com/catalog/product_info.php?products_id=2713

14

https://plenco.com/phenolic-novolac-resol-resins.htm

15

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=16&cad=rja&uact=8&ved=0ahUKEwifvMD2_cLWAhWGO5oKHaqqDxg4ChAWCEUwBQ&url=http%3A%2F%2Fwww.scielo.br%2Fscielo.php%3Fscript%3Dsci_arttext%26pid%3DS1516-14392015000601217&usg=AFQjCNGLxn7oISUQ3wAUKMs7QsK9T0oodQ

16

https://fire.nist.gov/bfrlpubs/fire94/PDF/f94092.pdf

17

https://journals.agh.edu.pl/mafe/article/view/1783

18

https://www.tandfonline.com/doi/abs/10.1080/00218464.2013.780971

19

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=20&cad=rja&uact=8&ved=0ahUKEwifvMD2_cLWAhWGO5oKHaqqDxg4ChAWCGUwCQ&url=https%3A%2F%2Ftspace.library.utoronto.ca%2Fbitstream%2F1807%2F36080%2F1%2FZhao_Yong_201306_PhD_thesis.pdf&usg=AFQjCNFXGfE42xGNgDM1eFDtmeDjDjzmLQ

20

https://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392015000601217

phenolic resin is a brittle polymers and have good thermal properties due to the presence of aromatic structure in their polymers chain, So in order to degradation with out using heat y using strong solution of sodium hydroxide.